Meter overpressure protection device

ABSTRACT

Disclosed is a gas meter-relief pressure device combination that maintains a predetermined pressure level in the meter and at a downstream combustion locus. The protection device, mounted on the gas meter itself, has: (1) an inlet orifice in communication with the interior of the gas meter; (2) a valve means normally closing the orifice; and (3) a vent, in communication with the orifice when the valve means is open. The diameter of the orifice is larger than the diameter of the gas vent. When a predetermined pressure is present in the meter, the valve begins to open and gas flows through the orifice and out the vent. Because the vent is smaller in diameter than the orifice, discharging gas builds up a back pressure that ultimately acts in tandem with the meter pressure to open the valve further than it would otherwise be opened if only the original meter gas pressure at the discharge end of the orifice was acting upon the valve.

United States Patent [1 1 Lofink METER OVERPRESSURE PROTECTION DEVICE [75] Inventor: Joseph P. Lofink, Hebron, Ohio [73] Assignee: Universal Lancaster Corporation,

Dallas, Tex.

[22] Filed: Apr. 5, 1972 [21] Appl. No.: 241,346

[52] US. Cl. 73/199 [51] Int. Cl. G01f 1/00 [58] Field of Search 73/198, 199, 201, 7

[56] 7 References Cited UNITED STATES PATENTS 1,855,682 4/1932 MacLean 73/199 X 3,500,826 3/1970 l-laire 73/199 X Primary Examiner--James J. Gill Attorney-Roy B. Moffitt Dec. 4, 1973 [57 ABSTRACT Disclosed is a gas meter-relief pressure device combination that maintains a predetermined pressure level in the meter and at a downstream combustion locus. The protection device, mounted on the gas meter itself, has: (1) an inlet orifice in communication with the interior of the gas meter; (2) a valve means normally closing the orifice; and (3) a vent, in communication with the orifice when the valve means is open. The diameter of the orifice is larger than the diameter of the gas vent. When a predetermined pressure is presentin the meter, the valve begins to open and gas flows through the orifice and out the vent. Because the vent is smaller in diameter than the orifice, discharging gas builds up a back pressure that ultimately acts in tandem with the meter pressure to open the valve further than it would otherwise be opened if only the original meter gas pressure at the discharge end of the orifice was acting upon the valve.

14 Claims, 4 Drawing Figures PAT DEC 41975 WED SHEET 10F 2 3775.035

FIGURE I l I I I I 7 I I7 I I I Ii I 5 l9 FIGURE 2 PATENTED DEC 4 ma SHEET 2 i]? 2 FIGURE 4 FIGURE 3 METER OVERPRESSURE PROTECTION DEVICE BACKGROUND OF THE INVENTION In the operation of gas appliances, it is common practice to distribute the gas in either one of two ways: at a relatively high or low pressure. In the high pressure mode of distribution, the gas is allowed to flow through a reducer means prior to entering a meter. Subsequent flow is to a combustion locus, such as gas burners, gas refrigerators or other appliances. For the purpose of reducing this high pressure gas to a lower pressure, prior to metering and subsequent combustion, a gas regulator is ordinarily used. The regulator, in turn, is ordinarily equipped on its low pressure or outlet side with some kind of pressure relief device to give relief in case of excessive pressure. In some cases, the pressure relief device is a liquid seal, usually composed of a liquid of a high specific gravity, such as mercury. The mercury is so placed that under the ordinary low pressure existing in the outlet pipe of the regulator, it remains in place. Should an excessive pressure be developed, the liquid is displaced, i.e., the seal is blown. Displacement of the liquid permits gas to escape via an outlet by bubbling up through the displaced mercury. Thus, the gas is discharged without injury to the downstream meter and combustion locus. I

Liquid-type safety devices of this type are known as disclosed by MacLean in U.S. Pat. No. 1,855,682; Witworth in U.S. Pat. No. 2,839,923; and Hutchinson in U.S. Pat. No. 2,274,697. Attention is also called to Smith, in U.S. Pat. No. 1,763,376. where a combination diaphragm and mercury-type regulator is disclosed. r

On the other hand, St. Clair, in U.S. Pat. No. 3,433,067 discloses a purely diaphragm-type regulator mounted on a meter.

SUMMARY OF THE INVENTION 1 Present-day technology and concern with consumer protection has created a public demand for ahigh capacity relief valve that would meet the stringentrequirements of the natural gas companies. These companies are becoming more and more safetyconscious because of the demands of the consumer, as reflected by the ever increasing. operating requirements of the United States Department of Transportation. To this end, the instant invention is directed.

Generally, the types of overpressure devices presently used fall into one of three classes. They are as follows:

1. High Pressure Shut-Off Valves Physically Placed in the Gas Line, designed to close at a predetermined pressure. Upon closure, this type valve will disrupt the flow of gas to the consumer. Such a valve has two major drawbacks, namely (a) flow disruption to the consumer can be costly to the gas company and (b) the valve itself is costly to install. Furthermore, the gas company would be liable to the consumer if a gas supply were to be cut off, due to an overpressure, and h the failure occurred in cold weather when the consumer was not at home.

2. Combination Service Regulator with an Internal Relief Valve. Such a combination would be adequate if used with house service where the regulator and internal relief valve combination has been I properly sized for the inlet pressure and regulator valve orifice. This particular approach has its limitations because there are a few conditions where the relief valve will be adequate to hold the service pressure under I psig that pressure desired when metering gas and supplying same to a combustion locus; and,

3. Mechanical Relief Valves in Service Lines. The adequacy of this particular approach has been proved, but it has the drawback of being costly to install.

Gas service using low pressure service to residences is only as safe as the low pressure system itself. Consequently, reliance upon a low pressure gas system per se fails to meet the problem of transient high pressures in a gas system.

The instant invention is a meter relief system mounted by four boltson the top of a gas meter replacing the conventional cover plate. The capacity of the relief meter is practically unlimited bacause the inlet .ori fice of the relief valve and vent can be made larger than the inlet of the meter itself.

With the relief valve gas meter combination, house service is protected from overpressure regardless of the type of gas system, whether it be l) a low pressure system; or (2) a high pressure'system. with a-service regulator. From the standpoint of economics, thedisclosed relief valve gas meter combination recommends itself because whatever service is encountered, the meter and service can be adequately protected from overpressure by simply and economically applying the relief valve directly to the top of the gas meter. This can be done without disturbing the service piping.

Other features and advantages of the invention will be apparent from the specification and claims when considered with connection with the accompanying drawings in which:

FIG. 1 is a plan view of the top of a conventional gas meter, modified by affixing thereto the disclosed meter overpressure protection device;

FIG. 2 is a combination gas meter andover-pressure protection device shown in cross sectionalong section line 2--2 of FIG. 1; and,

FIG. 3 is across section of a gas meter in combination with the disclosed overpressure protection device along section line 3-3 of FIG. 1. and

FIG. 4 is an elevation of a lifting tool that is used to manually lift thevalve shown in FIG. 3.

In 1, .thereis shown by reference element 1 a plan view of the top of a customary gas me'ter. Elements 18 and 17 indicate sidewalls of inlet and outlet ports respectively. A means for venting excess gas is shown by element 12. Bolts 11 are used to attach the meter overpressure protection device to the gas meter. An inspection plug is shown by element 9. Upon removal of the inspection plug, tool 10 (FIG. 4) can be inserted into spring plate 21 of FIG. 3. By lifting on the tool, once threadedly engaged in the central aperture in plate 21, the valve will be operated manually. This may be necessary for some gas companies where periodic inspections are required. The entire meter overpressure device can easily be removed for inspection of the gas meter itself (not shown).

FIG. 2 shows a cross section (front elevation) of that meter portion shown in FIG. 1 along sectional line 2-2. The meter chamber, shown at 4, is formed by sidewalls 15 and 16. Not shown in FIG. 2 is a gas measuring means,interposed between Chamber 4 and 14. Chamber 14 is communication with outlet 3 formed by sidewall 17. Chamber 4 is also in communication with inlet 2 formed by sidewalls 18. Additionally, chamber 4 is in communication with orifice 19 formed by sidewalls 5. A valve means (diaphragm type), shown at 7, is disposed above orifice 5 and is in its normally closed position as shown. Spring 8 is biased in such a manner that it is constantly pushing spring plate 21 and diaphragm 7 in a downward direction. Diaphragm 7 is made from some inert flexible material that will not stick to the orifice, for example, neoprene or other well-known materals. Capacity of the meter overpressure protection device is almost unlimited because the relief orifice l9 and vent 6 (FIGS) can be made larger than inlet 2.

In FIG. 3 there is shown a cross section along the section line 3-3 of FIG. 1. Meter chamber 4 communicates with a gas measuring means of conventional structure (not shown). Chamber 4 further communicates with orifice 19 formed by sidewalls 5. Orifice 19 and chamber 20 are sealed one from another by means of diaphragm 7 urged in the closed position by biasing spring 8. One end of spring 8 is positioned against top 23, the other end being positioned on spring plate 21. When in a normal position, spring 8 forces plate 21 and neoprene diaphragm valve 7 into close contact with the free ends of orifice walls 5, thereby blocking communication between orifice 19 and chamber 20. Neoprene diaphragm valve 7 not only extends across the diameter of orifice 19 but also extends further. Its terminal free edges are grasped by the sidewalls 24 of the meter overpressure protection device. Diaphragm valve 7 partially delimits chamber 20 which is in communication through channel 13 with exhaust chamber 21 formed by sidewall 12. Exhaust chamber 21a is in communication with the atmosphere via vent 6, formed by sidewalls 22. Upon compression of spring 8, diaphragm valve 7 reduces the volume of chamber 20 and compresses the gas (air) therein. Absent channel 13, this compression would retard the upward movement of diaphragm 7.

As will be more fully hereinafter explained, there is a definite area relationship between orifice 6 and 19, orifice 19 being larger in area than vent orifice 6.

OPERATION OF METER OVERPRESSURE PROTECTION DEVICE If, for any reason, high pressure gas should enter the inlet 2 of the gas meter 1, this pressure would exert an initial force on the valve area of the diaphragm 7 as circumscribed by sidewall 5 forming orifice 19. When the force of this pressure is greater than the force created by bias spring 8, e.g. 0.7 psig, the neoprene valve 7 will open, thereby allowing gas flow from meter chamber 4 to the outside atmosphere by way of exhaust chamber 21a andorifice 6. In this manner, excess gas will exhaust through exhaust chamber 21a and orifice 6 thereby maintaining a predetermined safe pressure in the gas meter 1. In turn, this will maintain a predetermined safe pressure at the outlet of the gas meter 1 as shown as element 3 formed by sidewall 17. As will be remembered, this is the outlet through which gas is piped directly to a combustion locus after being metered.

When the relief valve is closed, that is to say, in its normal position as shown by FIGS. 2 and 3, there is gas pressure only on the valve area of the diaphragm, namely that area circumscribed by sidewalls 5. Above the diaphragm in the spring area (chamber 20) and in chamber 21, there is atmospheric pressure.

As the valve 7 begins to open, two things happen; (1 the pressure in chamber 4 is applied across the entire expanse of diaphragm valve 7, not just that portion circumscribed by orifice sidewall 5, and (2) the pressure under the entire diaphragm 7 increases proportionally to the flow of gas because of a back pressure build-up resulting from the vent 6 orifice 19 size relationship. Applied to the entire surface of neoprene valve 7 is the additive force of the overpressure, appearing in meter chamber 4, plus that force from the derived back pressure in vent chamber 21a. This combined force compresses spring 8 and further opens the valve, allowing more gas to escape than would be otherwise absent any back pressure.

Because orifice area 19 is proportionally larger than vent 6, back pressure created by gas flowing in this structure increases as the flow increases. Obviously, the more the flow the more pressure is applied to the entire diaphragm 7. Spring 8 is calibrated to be compatible to this increased force to maintain a constant pressure in the meter chamber 4.

When the meter overpressure protection device is mounted on a gas meter in a normal horizontal position, as shown, the seat of orifice 19 formed by sidewalls 5 is higher than the vent opening. This feature will enable any condensation forming in the vent chamber to drain out the vent. This protects the valve and orifice from freezing shut.

Typical regulator and meter service to a residence comprises a 4-inch street main carrying gas at 20 pounds pressure and a l l/4 inch service line. A service regulator is placed in the service line just upstream from the meter to service the residence. It reduces the street main pressure (20 pounds) to 4 ounces of pressure before the gas enters the meter. Gas then flows through the meter and subsequently distributed to various appliances in the house.

Theamount of gas passing through a meter is dependent upon the requirements of the appliances served. If all of the appliances are off, the regulator and meter are passing a very small amount of gas, namely that to satisfy pilot lights. If all the appliances are on, the regulator and meter could be operating at maximum capacity.

Regulators usually fail when the regulator is operating at maximum capacity. For example, a piece of foreign material lodges between the regulator orifice and valve. This causes no problem until use of the appliances are reduced. When this occurs, pressure builds up and the regulator begins to close ofi; howevwr, the regulator cannot close because of the foreign material. If there is no relief valve, and the demand cuts back to minimum flow, the required 4-ounce pressure in the meter and house could increase to the 20 pounds line pressure. The meter overpressure device of the instant invention is designed to obviate just such a problem. It can be used either by itself or in combination with a regulator upstream from the protection device meter combination. Certain data has been observed using a gas meter in combination with a meter overpressure protection device in combination with a standard gas regulator upstream. In these cases, the meter relief valve combination had a 1 V4 inch orifice 19 and one inch vent orifice 6, with the spring 8 regulated to compress at 0.7 psig. Such a combination was used with a One inch regulator with valve assembly removed l inches 6 inches l20 psi air source One inch hand valve Gauge A Meter over pressure protection device plus meter 6 inches Gauge B By slightly opening the hand valve and allowing air to pass through the system, a soap bubble was allowed to be formed across the vent 6 of the meter overpressure protection device. Flow was increased through the hand valve by slowly opening same to increase the pressure in the system. When Gauge B registered 10 ounces of pressure, the soap' bubble on vent 6 broke. This identified the point that the overpressure meter protection device started to leak. At this point, the force of the air acting against that area of diaphragm Tcircumscn'bed by element equals the force working in the opposite direction created by spring 8. Leak point at ounces is 6 ounces above the normal 4 ounce operating pres sure. At this point (10 ounces), the flow of gas through the meter relief overpressure device is not enough to cause a measurable back pressure, vent 6 orifice 19 co acting with gas flow there through.

The hand valve was opened .further until 10 pounds of pressure was registered on Gauge A. At this point, Gauge B registered 0.7 pounds. It was observed that under these conditions, the meter overpressure device was not completely open; however, back pressure was beginning to build on the underside of diaphragm 7.

The hand valve was opened still further until Gauge A registered 20 pounds of pressure. Under these conditions, Gauge B read 0.6 pounds pressure, and the meter overpressure device was wide open with the back pressure in the device eserting a force over the entire area of the diaphragm 7. The 0.6 pounds pressure at 20 pounds inletpressure versus the 0.7 pounds pressure at 10 pounds inlet pressure can be explained.

It will be recognized that spring 8 was precompressed to balance 10 ounces of pressure in the orifice chamber 19. There is zero pressure (gauge) above the entire diaphragm and the area outside theorifice on the underside of the diaphragm. To move diaphragm 7 upwardly, spring 8 must be compressed. As spring 8 is compressed it gains force. If there were no structure in the meter overpressure device to take advantage of any back pressure, it would take about one and one quarter pounds of pressure in chamber 4 to open. the diaphragm 7 as wide as ten ounces of gas pressure would do using the meter overpressure device.

By using the structure of the meter overpressure device as disclosed, an, additional force opposes the spring, that force being the back pressure created by gas flowing through orifice 19 and vent 6. The reason for the pressure drop from 0.7 pounds to 0.6 pounds in the data below is that the additional force derived from the back pressure applied to that diaphragm area not circumscribed by sidewalls 5 increased at a faster rate than the spring force. It will be remembered, that the back pressure increase is directly proportional to the flow of gas through the meter overpressure device.

When Gauge A reads 30 pounds, Gauge B reads 0.9 pounds. At 40 pounds (Gauge A), Gauge B reads 1.3 pounds. When Gauge A reads 20 pounds the overpressure valve was wide open and no longer controlling. Thus, when the meter overpressure device is wide open, the meter pressure will increase with the inlet pressure. The following data was taken using the procedures and equipment set forth above.

% Orifice in Regulator lnlet of Regulator and Meter Chamber psig I0 Pressure in Meter psig A Orifice in Regulator lnlet of Regulator and Meter Chamber psig Pressure in Meter psi -.g..... OOQOOWMQ lnlet of Regulator and Meter Chamber psig Pressure in Meter psig aol'moscsosc'wo Maximum recommended inlet pressure with specified orifice.

Depending on the orifice size and regulator, the meter overpressure protection device will protect the meter and combustion locus from excessive pressures with relative ease, depending of course on the particular orifice size of the regulator employed. If it were not for the size relationship between orifice l9 and vent orifice 6, it would take about one and one quarter psig of gas pressure in chamber 4 to open valve 7 the same dis.- tance as 10 to 12 ounces would, using the structure as disclosed. Simply stated, the disclosed overpressure device achieves a greater valve opening per pound of gas pressure in comparison to a structure having no like size relationship between valve orifice 19 and vent 6. Channel 13 allows communication between chamber 20 and 21a. The size of channel 13 is relatively small in comparison to the size of passageway 21 and the volume of chamber 20. Channel 13 acts as somewhat of a damper and a smoothing feature for the action of diaphragm 7. By not venting chamber 20 to the atmosphere, damage to the diaphragm 7 and spring 8 is avoided as a result of freezing weather (water) and foreign objects. Pressure in chamber 20 and passageway 21a would attempt to equalize if channel 13 were large enough. However, such has not been found to be the case where the size relationship of channel 13 is relatively small.

I claim:

1. In combination with a gas meter having an inlet port, an outlet port and an internal gas-receiving chamber between said ports, a pressure relief valve comprising an orifice in fluid communication with said chamber, a relief passageway having a vent, and movable, pressure responsive valve closure means having one side exposed to gas pressure in said chamber for controlling flow of gas through said orifice by movement toward and away from said orifice, said valve closure means being movable to a position to block flow of gas through said orifice, the area of said one side which is exposed to gas pressure when said valve closure means is positioned to allow gas to flow through said orifice being greater then the area that is exposed to gas pressure in said chamber when said valve closure means is in the position where it blocks flow of gas through said orifice, said orifice providing fluid communication between said chamber and said passageway to allow gas from said chamber to flow through said passageway and said vent when said valve closure means is moved to a position that allows gas to flow though said orifice, said orifice having a flow passage area that is greater than that of saidvent to provide a back pressure that is created by gas flow through said vent, said one side of said valve closure means being exposed to acted upon by said back pressure to move in a direction that allows for increased flow of gas through said orifice.

2. The combination defined in claim 1 comprising spring means yieldably biasing said valve closure means to its position where it blocks flow of gas through said orifice.

3. The combination defined in claim 2 wherein said valve closure means comprises a flexible diaphragm, wherein said orifice is defined by a tubular portion, and wherein said diaphragm is biased by said spring means to seat against an end of said tubular portion to block flow of gas through said orifice. I

4. The combination defined in claim .3 comprising bottom and side wall portions cooperating with said diaphragm to define a vent chamber that receives said tubular portion, said bottom wall portion separating said vent and gas meter chambers, and said side wall portion having an outlet opening to provide for fluid communication between said vent and said vent chamber, said tubular portion extending upwardly from said bottom wall portion, and said end of said tubular portion being disposed at a level'that is above the lower portion of said outlet opening.

5. The combination defined in claim 1 whereinthe size of said inlet port is smaller than that of said orifice.

6. The combination'defined in claim 1 wherein the size of said inlet port is smaller than that of said vent.

7. The combination defined in claim 6 wherein the size of said inlet port is smaller than that of said orifice.

8. In combination with a gas meter having an inlet port, an outlet port and an internal gas-receiving chamber between said ports, a pressure relief valve comprising an orifice in fluid communication with said chamber, a relief passageway having a vent, movable, pressure responsive valve closure means having one side exposed to gas pressure in said chamber for controlling flow of gas through said orifice by movement toward and away from said orifice, said orifice providing fluid communication between said chamber and said passageway to allow gas from said chamber to flow through said passageway and said vent when said valve closure means is moved to a position that allows gas to flow thorugh said orifice, and means biasing said pressure responsive means to a position to block flow of gas through said orifice when the gas pressure in said chamber is less than a predetermined amount, said pressure responsive means being responsive to gas pressure in said chamber to move away from said orifice and thereby to allow for flow of gas through said orifice when the gas pressure in said chamber becomes at least equal to said predetermined amount, said orifice cooperating with said pressure responsive means to expose an area of said one side to gas pressure in said chamber that is less than the area that is exposed to gas pressure when said pressure responsive means is moved away from its gas flow-blocking position to allow gas to flow through said orifice, said orifice having a flow passage area that is greater than that of said vent to provide a back pressure that is created by gas flow through said vent, said one side of said valve closure means being exposed to and acted upon by said back pressure to move in a direction that allows for increased flow of gas through said orifice.

9. A gas meter pressure relief valve comprising an orifice adapted to be in fluid communication with an intemal chamber in a gas meter, a relief passageway having a vent, and pressure responsive means having one side arranged to' be exposed to gas pressure in said chamber for controlling flow of gas through said orifice, said pressure responsive means being movable between closed and opened positions to respectively block and provide for flow of gas through said orifice, said orifice providing fluid communication between said chamber and said passageway when said pressure responsive means is opened to allow gas from said chamber to flow through said passageway and said vent, the area of said one side which is exposed to gas pressure when said pressure responsive means is positioned to allow gas to flow, through said orifice being greater than thearea that is exposed to the chamber gas pressure when said pressure responsive means is in its position where it blocks flow of gas through said orifice, said orifice having a fluid passage area that is larger than that of said vent to provide a back pressure that is created by the flow of gas through said vent, and said back pressure acting on said pressure responsive means to urge said pressure responsive means in a direction that allows for increased gas flow through said orifice.

10. The gas meter pressure relief valve defined in claim 9 comprising spring means yieldably biasing said pressure responsive means to its position where it blocks flow of gas through said orifice.

11. The gas meter pressure relief valve defined in claim 10 wherein said orifice is defined by a tubular portion, and wherein said pressure responsive means comprises a flexible diaphragm that is biased by said spring means to seat against one end of said tubular portion to block flow of gas through said orifice.

12. The gas meter pressure relief valve defined in claim 11 comprising side and body wall portions cooperating with said diaphragm to define a vent chamber, said relief passageway being in communication with said vent chamber to provide a side outletfor said vent chamber, said tubular portion extending upwardly from said bottom wall portion and having said one end disposed at a level that is higher than the lower portion of 14. The gas meter pressure relief valve defined in claim 13 wherein said plate has an opening that is adapted to receive a tool for manually lifting said diaphragm away from said tubular portion, and manually removable means carried by said cover to provide for the insertion of said tool to lift said diaphragm without removing said cover. 

1. In combination with a gas meter having an inlet port, an outlet port and an internal gas-receiving chamber between said ports, a pressure relief valve comprising an orifice in fluid communication with said chamber, a relief passageway having a vent, and movable, pressure responsive valve closure means having one side exposed to gas pressure in said chamber for controlling flow of gas through said orifice by movement toward and away from said orifice, said valve closure means being movable to a position to block flow of gas through said orifice, the area of said one side which is exposed to gas pressure when said valve closure means is positioned to allow gas to flow through said orifice being greater then the area that is exposed to gas pressure in said chamber when said valve closure means is in the position where it blocks flow of gas through said orifice, said orifice providing fluid communication between said chamber and said passageway to allow gas from said chamber to flow through said passageway and said vent when said valve closure means is moved to a position that allows gas to flow though said orifice, said orifice having a flow passage area that is greater than that of said vent to provide a back pressure that is created by gas flow through said vent, said one side of said valve closure means being exposed to acted upon by said back pressure to move in a direction that allows for increased flow of gas through said orifice.
 2. The combination defined in claim 1 comprising spring means yieldably biasing said valve closure means to its position where it blocks flow of gas through said orifice.
 3. The combination defined in claim 2 wherein said valve closure means comprises a flexible diaphragm, wherein said orifice is defined by a tubular portion, and wherein said diaphragm is biased by said spring means to seat against an end of said tubular portion to block flow of gas through said orifice.
 4. The combination defined in claim 3 comprising bottom and side wall portions cooperating with said diaphragm to define a vent chamber that receives said tubular portion, said bottom wall portion separating said vent and gas meter chambers, and said side wall portion having an outlet opening to provide for fluid communication between said vent and said vent chamber, said tubular portion extending upwardly from said bottom wall portion, and said end of said tubular portion being disposed at a level that is above the lower portion of said outlet opening.
 5. The combination defined in claim 1 wherein the size of said inlet port is smaller than that of said orifice.
 6. The combination defined in claim 1 wherein the size of said inlet port is smaller than that of said vent.
 7. The combination defined in claim 6 wherein the size of said inlet port is smaller than that of said orifice.
 8. In combination with a gas meter haviNg an inlet port, an outlet port and an internal gas-receiving chamber between said ports, a pressure relief valve comprising an orifice in fluid communication with said chamber, a relief passageway having a vent, movable, pressure responsive valve closure means having one side exposed to gas pressure in said chamber for controlling flow of gas through said orifice by movement toward and away from said orifice, said orifice providing fluid communication between said chamber and said passageway to allow gas from said chamber to flow through said passageway and said vent when said valve closure means is moved to a position that allows gas to flow thorugh said orifice, and means biasing said pressure responsive means to a position to block flow of gas through said orifice when the gas pressure in said chamber is less than a predetermined amount, said pressure responsive means being responsive to gas pressure in said chamber to move away from said orifice and thereby to allow for flow of gas through said orifice when the gas pressure in said chamber becomes at least equal to said predetermined amount, said orifice cooperating with said pressure responsive means to expose an area of said one side to gas pressure in said chamber that is less than the area that is exposed to gas pressure when said pressure responsive means is moved away from its gas flow-blocking position to allow gas to flow through said orifice, said orifice having a flow passage area that is greater than that of said vent to provide a back pressure that is created by gas flow through said vent, said one side of said valve closure means being exposed to and acted upon by said back pressure to move in a direction that allows for increased flow of gas through said orifice.
 9. A gas meter pressure relief valve comprising an orifice adapted to be in fluid communication with an internal chamber in a gas meter, a relief passageway having a vent, and pressure responsive means having one side arranged to be exposed to gas pressure in said chamber for controlling flow of gas through said orifice, said pressure responsive means being movable between closed and opened positions to respectively block and provide for flow of gas through said orifice, said orifice providing fluid communication between said chamber and said passageway when said pressure responsive means is opened to allow gas from said chamber to flow through said passageway and said vent, the area of said one side which is exposed to gas pressure when said pressure responsive means is positioned to allow gas to flow through said orifice being greater than the area that is exposed to the chamber gas pressure when said pressure responsive means is in its position where it blocks flow of gas through said orifice, said orifice having a fluid passage area that is larger than that of said vent to provide a back pressure that is created by the flow of gas through said vent, and said back pressure acting on said pressure responsive means to urge said pressure responsive means in a direction that allows for increased gas flow through said orifice.
 10. The gas meter pressure relief valve defined in claim 9 comprising spring means yieldably biasing said pressure responsive means to its position where it blocks flow of gas through said orifice.
 11. The gas meter pressure relief valve defined in claim 10 wherein said orifice is defined by a tubular portion, and wherein said pressure responsive means comprises a flexible diaphragm that is biased by said spring means to seat against one end of said tubular portion to block flow of gas through said orifice.
 12. The gas meter pressure relief valve defined in claim 11 comprising side and body wall portions cooperating with said diaphragm to define a vent chamber, said relief passageway being in communication with said vent chamber to provide a side outlet for said vent chamber, said tubular portion extending upwardly from said bottom wall portion and having said one end disposed at a level that is higher than the lower porTion of said side outlet.
 13. The gas meter pressure relief valve defined in claim 11 comprising wall means cooperating with said diaphragm to define a vent chamber which is in fluid communication with said relief passageway, said orifice opening into said vent chamber, and a cover mounted on said wall means, said spring means being compressed between said cover and a plate that is fixed to said diaphragm.
 14. The gas meter pressure relief valve defined in claim 13 wherein said plate has an opening that is adapted to receive a tool for manually lifting said diaphragm away from said tubular portion, and manually removable means carried by said cover to provide for the insertion of said tool to lift said diaphragm without removing said cover. 